Thrust-relieved propeller



Patented July 12, 1938 UNITED STATES PATENT OFFICE 9 Claims.

This invention relates to all kinds of screwtype uid impellers, such as wind mills, ofce fans, and propellers, and particularly to aerial propellers. I will describe the invention in most part as applied to the latter, the application to the other members of this class of impellers follows therefrom by analogy.

'I'he invention consists in relieving the propeller from a portion of its axial airforce component, ordinarily called thrust, which hasA to be produced, by the provision of an airfoil or airfoils, preferably ring shaped airfoils in concentric relation to the propeller axisA and positioned adjacent or not very far off the course of the propeller blade tips. These airfoils, in keeping with the well known principles and practices of airfoil design, are so shaped and so inclinedv relative to the airow attributable to the motion and rotation of the propeller, as to produce or experience an air-force component parallel and in the same direction as the propeller thrust, whereby the airfoil furnishes itself that portion of the total thrust by which the propeller has been relieved. With a stationary propeller, this component may constitute the entire airforce of the several airfoil elements.

With a traveling propeller, however, this conedge or nose gently rounded. This leads to ccn-` ventional modernu eflicient wing sections with inwardly directed suction side for aerial propellers, as with them the undisturbed airflow' is almost straight. With stationary fans, this may lead to extremely curved wing sections, ras then the undisturbed streamlines are themselves strongly curved. The undisturbed air should impinge on` the airfoil section of aerial propellers from the outside. This does not necessarily require an inwardly and conically directed zero-lift line of the wing section, because the undisturbed airflow itself is converging. Hence, a wing section parallel to the axis is already inclined in the indicated manner relative to the undisturbed propeller airflow.

The object of the invention is to provide for a propeller assembly having superior eiliciency, lighter weight, smaller manufacturing costs, and above all a smaller propeller tip speed by virtue of which the almost unbearable propeller noise of present day airplanes is reduced to a reasonable amount. For stationary airfoils are more efficient and less noisy than rapidly rotating propeller` blades, and the thrust relief exerted by the stationary airfoils makes it feasible to em- (cl. 17o- 168) ploy a propeller of smaller diameter and hence, at the same rotational speed, with smaller tip velocity than an unrelieved propeller would have, whereby the chief source of excessive noise is eliminated. v

These and other objects and advantages of the present invention will be described in the following specification and illustrated in the accompanying drawing, preferred embodiments being shown for illustratipn only, for, since the very broad principlesof my invention can be incorporated in many specific devices, it is not intended to be limited to the ones shown, except as such limitations are clearly imposed by the appended claims.

In the drawing, equal characters refer to similar parts throughout the several views, of which Fig. 1 shows an aerial propeller in sideview, with its relieving ring in cross section,

Fig. 2 shows the same propeller and ring assembly seen from the rear, l

Fig. 3 is a diagram illustrating the determination of the zero lift direction of a wing section, and

Figs. 4 to 9 show the upper half of the propeller of Fig. l in the same view but somewhat larger scale, and different types of relieving rings in cross section.

In Figs. l and 2 there is shown an engine housing 20 fixed to an airplane not shown in the drawing, an engine shaft Il, a four blade pusher propeller I0 mounted on shaft Il having propeller tips I2, rods 2l mounted on engine housing 20, and an airfoil 30 the same being a closed circular ring and hence arched and looped. The axis of ring 30 coincides with the axis of shaft Il. Arrow N represents the motion of the airplane relative to the air. Arrows L M represent schematically the motion of the 'airpast the propeller disregarding the interference of ring 30, but taking into account the motion and the rotation of the propeller. Arrows L-M indicate a converging ow. As shown in Fig. 4, ring 30 surrounds the propeller with suitable clearance. This has not to be particularly small, a reasonable vicinity of ring 30 to the tip circle l2 is all that is required. It is also not material whether the ring is slightly in front of, co-planar with, or behind the propeller. The axial length of ring 30, the same being the chord length of itsV wingsection, is much smaller than the circumference of the ring, whereby the airfoil possesses a. large aspect ratio, i. e. the circumferential span divided by the chord. 'I'he wing section of ring 30 is a so-called strut section, rounded at the leading edge K, which is at the left of Fig. 4,

and having a sharp trailing edge T. The thickness is gradually varying, and larger in front than in rear. The axis of wing section Fig. 4 is parallel to the propeller axis. The undisturbed airflow would have the direction such as L M, and hence would impinge on the outside of the ring.

Figs. 5 to 8 diiler from Fig. 4 by the wing sections of the ring only. In'Flg. 5, the wing section is the same as in Fig. 4, except that the section axis is conically inclined, whereby the impinging angle relative to airflow L-M is increased. In Fig. 6 the wing section is unsymmetrical, the lower or pressure and less or even concavely curved camber line being on the outside. This ring is shown in front of the propeller plane, to illustrate another one of the several positions in which the rings will be effective. This position is not in direct relation to the wing section employed, but will be chieiiy determined from general design considerations. Fig. '7 shows two rings in tandem relation, and Fig. 8 two in biplane relation, ring 34 surrounding ring 3l, Whereas ring33 is in front of ring 33. The inside diametenof rings 30, 3|., 32 and 34 is larger than the; propeller diameter of I0. The inside diameteroi rings 33 and 33 is shown to be just slightly smaller than the diameter of propeller IU, the two rings 33 and 33 being in front and in rear respectively of the propeller. Bplane rings 34 and 34 illustrate the ring being located in rear of the propeller plane.

Fig. 9 illustrates a stationary propeller, such as an oice ian. The undisturbed airflow of such propeller near its tips has the general character of curved line LM of Fig. 9. For that reason, a strongly curved wing section 35 is then in order, the rounded leading edge K outside.

In Fig. 3, a wing section is represented, having the leading edge K and the trailing edge T. For the purpose of the specification, the direction of the zero lift-line G-T of any such section may be determined by connecting the trailing edge T with the center C of the section, the latter being determined by the conditions DE=EF, and AC=BC. GT represents the direction of the wing section for the purpose of this specification. 'I'he lift produced is directed broadly from L towards G, and more or less at right angles to LM.

With a wind mill, the airflow will be divergent, not convergent as in Fig. 1. The structural arrangement of Fig. 4 would not be suitable for a wind mill, because a divergent flow line LM would impinge on ring 30 from inside, not from outside as in Fig. 4. A divergent conical ring as in Fig. 5, or better as in Fig. 6, would be required.

In operation as an aerial propeller, the ring will relieve the propeller by a portion of the total thrust. At low speeds, before and during take-off, the portion by which the propeller is relieved will be considerably larger than at high speeds; but at these high speeds, less relief is necessary as the maximum thrust then available is anyhow.

smaller than at low speeds. At these lower speeds, the relieving airfoil will also bring about that the propeller absorb more horsepower than without it, whereby the available power supply is utilized to better advantage.

I claim:

1. The combination of an aerial power-driven screw-type propeller and a stationary ring posi- ,tioned adjacent the course of the propeller tips,

said ring having a smooth, continuous, sharply trailed wing section contour, the zero-lift direction thereof being outwardly and rearwardly inclined relative to the direction oi the propeller axis. j

2. The combination of an aerial power-driven screw-type propeller and a plurality of stationary rings positioned adjacent the course of the propeller tips, said rings having a(v smooth, continuous, sharply trailed wing section contour, the zero-lift direction of the contour of at least one of said rings being outwardly and rearwardly inclined relative to the direction of the propeller axis.

3. The combination of a screw-type power driven uid propeller and a stationary arch positioned adjacent the course of the propeller tips, said arch having a smooth continuous sharply trailed wing section contour the zero lift direction thereof being outwardly and rearwardly inclined relative to the flow produced by the propeller.

4. The combination of a screw-type powerl driven iiuid propeller and a stationary ring positioned adjacent the course of the propeller tips, said ring having a smooth continuous sharply trailed wing section contour the zero lift direction thereof being outwardly and rearwardly inclined relative to the ow produced by the propeller.

5. The combination of a screw-type power driven propeller and a plurality of stationary rings positioned adjacent the course of the propeller tips, said rings having a smooth continuous sharply trailed wing section contour, the zero lift direction of at least the contour of one of said rings being outwardly and rearwardly inclined relative tb the iiow produced by the propeller.

l6. The combination of an aerial propeller and a statonary large-aspect-ratio thrust relieving ring positioned adjacent the course of the propeller tips, having smooth. continuous sharply trailed wing section contours with their zero lift direction rearwardly and outwardly inclined relative to the air ow.

7. The combination of a power driven screwtype propeller and a stationary ring positioned adjacent the course of the propeller tips, said ring having a smooth, Acontinuous sharply trailed cambered wing section contour, the zero lift direction thereof being outwardly and rearwardly inclined relative to the propeller axis and the mean camber being concave when viewed from outside the ring, convex when viewed from the axis.

8. The 'combination of a power driven screwtype propeller and a stationary ring positioned adjacent the course of the propeller tips, said ring having a smooth, continuous sharply trailed wing section contour, the zero lift direction thereof being outwardly and rearwardly inclined relative to the propeller axis. the maximum diameter of the ring being larger than the maximum propeller diameter.

9. The combination of a screw-type power driven fluid propeller and a stationary ring positioned adjacent the course of the propeller tips, said ring having a smooth continuous sharply trailed wing section contour. the line connecting the trailing edge of said contour with its center of section being outwardly and rearwardly inclined relative to the iiow produced by the propeller.

MAX M. MUNK.

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